Surface detectors of the TAx4 experiment

Telescope Array (TA) is the largest ultrahigh energy cosmic-ray (UHECR) observatory in Northern Hemisphere. It explores origin of UHECRs by measuring their spectrum, arrival-direction distribution, and mass composition using a surface detector (SD) array covering approximately 700 km2 fluorescence (FD) stations. TA has found evidence for cluster cosmic rays with energies greater than 57 EeV. In order to confirm this more data, it necessary increase data collection rate. We have begun building an expansion that we call TAx4. paper, explain motivation, design, technical features, expected performance TAx4 SD. also present TAx4’s current status examples already been collected.